JPH01302997A - Acoustic device - Google Patents

Abstract

PURPOSE:To effectively reproduce a low-pitched sound even though a device is miniaturized by making a vibrator driving device control a driving state so as to reduce or invalidate internal impedance peculiar to a vibrator equivalently. CONSTITUTION:When a drive signal is given to the transducer 22 of the vibrator 20 from the vibration driving device 30 with a negative impedance driving function, the transducer 22 electromechanical-converts it, and reciprocates a vibration diaphragm 21 right and left in a figure and makes a mechanical sound. Thus, the internal impedance peculiar to the transducer 22 is reduced effectively. Accordingly, the transducer 22 drives the diaphragm as responding faithfully to the drive signal from the device 30, and gives driving energy independently to a Helmholtz resonator 10. At this time, the left surface side of the diaphragm 21 in the figure forms a direct emitting part for emitting the sound directly toward an external part, and the right surface side of the diaphragm forms a resonator driving part to drive the resonator 10. Thus, the sound of the diaphragm 21 is emitted directly, and the air of the resonator 10 is made to resonate, and a heavy and low-pitched sound is resonant-emitted from a resonant emitting part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acoustic device including a resonator.

[Conventional technology]

A speaker unit as a type of audio device is generally configured such that a speaker unit (vibrator) is placed in a cabinet and is driven by an amplifier (AMP). Of the reproduction characteristics, especially the bass reproduction characteristics, are mainly determined by the volume of the cabinet.

An electrodynamic direct radiation speaker (dynamic cone speaker), which is a typical example of a direct radiation speaker, has a substantially conical diaphragm, and this diaphragm has a magnetic gap attached near the top of the cone. It is driven by the voice coil inside. When such a speaker is used in an audio device, sound is emitted directly from the front surface of the diaphragm, but sound waves are also emitted from the rear surface. By the way, the sound waves from both the front and rear sides are in opposite phases, so if the difference in the path of the sound waves from the front and rear sides to the listener is around an odd multiple of a half wavelength, the sound pressure from both sides will be in the same phase. and are superimposed on each other.

However, when this distance difference is around an even multiple of a half wavelength, the sound pressures cancel each other out and weaken each other, so considering that the speakers emit sounds of various wavelengths, the sound from the rear is not heard by the listener. It is desirable to prevent the sound from reaching the front, or to prevent the sound from the rear from having a negative effect on the sound radiated directly from the front.

Therefore, something called a baffle is used in direct radiation speakers. As devices that block the flow of sound in front and behind the diaphragm, there are known flat baffles, open-back box-shaped baffles, and closed-type baffles as shown in Figure 29, but the purpose is slightly different from these. As shown in FIG. 31, a phase inversion type baffle (bass reflex type) is known. These will be explained in order below.

FIG. 29(a) is a cross-sectional view of the plane baffle.

As shown in the figure, a hole of the same size as the vibrator is made in one wide flat plate 1, and a substantially conical diaphragm 2 is attached to the hole. An electrodynamic electroacoustic transducer (speaker) 3 including a voice coil, a magnetic circuit, etc. is attached to the conical top of the diaphragm 2. According to this planar baffle, sound from the rear surface is blocked by the flat plate 1, so if the flat plate 1 were made infinitely wide, the baffle effect would be complete. However, this is unrealistic, and in reality, a flat plate 1 of a finite size is used. However, for example, if the lowest frequency of the sound pressure reproduction characteristics is set to about 60 hertz,
The size of the flat plate 1 is about 2 m on one side, which is not practical.

FIG. 29(b) is a sectional view of the rear open box baffle.

As shown in the figure, a hole is made in the front of the box 4 which is open at the rear, and a vibrator consisting of a diaphragm 2 and an electrodynamic speaker 3 is attached to the hole. However, even with this box-shaped baffle with an open rear surface, the size becomes too large to obtain the necessary degree of baffle effect, and the air column of the box body 4 constitutes a resonant system, which deteriorates transient characteristics.

FIG. 29(C) is a sectional view of the closed baffle.

As shown in the figure, a hole is made in the front of the sealed box 5, into which a vibrator consisting of a diaphragm 2 and an electrodynamic speaker 3 is attached. In this structure, if the box body 5 does not vibrate at all, the sound from the rear surface of the diaphragm 2 is completely confined, and a perfect baffle effect can be obtained. However, the air inside the box body 5 acts as an air spring and imparts elasticity to the diaphragm 2, making the overall resonant frequency higher than that of a flat baffle.

This will be explained with reference to FIG. The same figure is Figure 29 (C)
1 is a simplified electrical equivalent circuit diagram of the system of FIG. R in the figure is the voice coil DC resistance of the vibrator, and m, S, and S correspond to m - equivalent mass of the vibration system S → equivalent stiffness of the vibration system S → equivalent stiffness of the box body, respectively. There is a relationship where Also, A is the force coefficient, B is the magnetic flux density in the magnetic gap of the magnetic circuit,
It is obtained as A=Bρ, where ρ is the length of the voice coil. The parallel resonant circuit Z1 based on the equivalent motional impedance of the unit vibration system and the equivalent motional impedance A2/S of the sealed box are connected in parallel with each other, and these are connected to the amplifier ( (Illustrated in the figure)) are connected in parallel.

As is clear from this electrical equivalent circuit, the resonant frequency f of the entire system rises above the lowest C resonant frequency of the vibrator, and f = f (1+S /S )oc
oc.

The equivalent Q value C (Q) at the resonant frequency f is the OC at the lowest resonant frequency f of the vibrator.
For the Q value (Q), Q=Q (1+S/S)OCOCO increases. Therefore, in order to improve the low-frequency reproduction characteristics, the equivalent stiffness of the box must be made smaller, which forces the cabinet to be larger.

The bass reflex type speaker system is slightly different in purpose from these, and its perspective view and sectional view are shown in Figure 3. As shown in the figure, a hole is made in the box 6 and a vibrator consisting of a diaphragm 2 and an electrodynamic speaker 3 is attached.
Further, an open port 8 having a sound path 7 is provided below.

Here, in a bass reflex type speaker system that follows normal basic settings, the resonance frequency (resonance frequency) f due to the air spring inside the box body 6 and the air mass of the sound path 7 is determined by incorporating the vibrator into the bass reflex type box body. It is set lower than the lowest resonant frequency f of the vibrator (speaker) in the p state. At a frequency higher than the resonance frequency due to the above-mentioned air splash and air mass, the sound pressure from the rear surface of the diaphragm 2 has an opposite phase at the sound path 7.
Therefore, in the front of the box body 6, the sound radiated directly from the front surface of the diaphragm 2 and the sound from the opening □ port 8 end up in the same phase, and the sound pressure is strengthened. As a result, with the optimally designed bass reflex speaker system, the frequency characteristics of the output sound pressure can be extended to below the low resonance frequency of the vibrator, and as shown by the two-dot chain line in FIG. The regeneration range can be wider than that of an infinite plane baffle or a closed baffle.

However, when trying to achieve uniform reproduction with this bass reflex speaker system, the resonance Q of the unit vibration system
There are various constraints regarding values, etc., and the characteristics shown in FIG. 32 are obtained only when these constraints are satisfied. As described above, it has been extremely difficult to obtain optimal design conditions for bass reflex type speaker systems for boat fishing.

On the other hand, an attempt is sometimes made to intentionally lower the resonant frequency f 2 on the resonator side to an extremely low level, focusing only on the acoustic radiation ability from the open port, without being particular about the basic design concept of the bass reflex speaker system.

OP However, since the volume of the cabinet is closely related to the bass reproduction ability, it is necessary to increase the volume in order to achieve higher bass reproduction, as is the case with closed baffles, although there are differences in degree. We had no choice but to make it a shaped cabinet (box).

This situation will be explained in more detail with reference to FIG.

First, the bass reflex type speaker system shown in FIG. 31 is shown as a simplified electrical equivalent circuit as shown in FIG. 33. In the same figure, A, R.

■ m, S, mg and S. is the same as shown in FIG. 30, and mg corresponds to the equivalent mass of the sound path (port). The parallel resonant circuit Z1 based on the equivalent motional impedance of the unit vibration system and the series resonant circuit Z2 based on the equivalent motional impedance of the port resonance system are connected in parallel with each other. It is connected in parallel to a driving amplifier (not shown) via the drive amplifier (not shown).

As is clear from this electrical equivalent circuit, a major feature of the bass reflex speaker system is that the resonance system is two-dimensional.
There are two. This exhibits a bimodal characteristic in terms of impedance characteristics, and there are a total of three resonance points: the peaks of the two peaks and the valley between them, and the resonance at these valleys corresponds to the port resonance system (as mentioned above) In terms of shape, there was only one resonant system, the impedance characteristics were unimodal, and there was only one resonance point). In this bass reflex speaker system, the voice coil resistance R of the vibrator (unit) is the braking resistance of the parallel resonant circuit Z1 on the vibrator side and the braking resistance of the series resonant circuit Z2 on the open port (duct) side. Also serves as. Therefore, the parallel resonant circuit Z 1 and the series resonant circuit Z2 interfere with each other.

As an example of mutual interference or mutual dependence, for example, if a vibrator with a strong magnetic circuit is used, the Q value of resonance as a vibrator will be small, whereas the Q value of resonance on the open port side will be small. On the other hand, when a vibrator with a weak magnetic circuit is used, a completely opposite change can occur. In the original design of a bass-reflex speaker system, it was necessary to select an optimal point that would provide a -like low frequency reproduction characteristic under such conflicting and mutually dependent conditions.

Now, when considering reducing the volume of the cabinet,
The lowest resonant frequency f 2 of the unit vibration system shows the same tendency as in the case of a closed baffle, and as a result, the lowest resonant frequency f 2 becomes higher. Ultimately, the acoustic radiation effect of the open port will again improve the bass reproduction characteristics to some extent, but if you consider the system as a whole, even if you are using a bass reflex speaker system, the smaller the cabinet, the better. It is inevitable that the bass range reproduction ability will decrease.

In particular, when the resonant frequency f of the port resonance system is intentionally lowered from the basic settings as mentioned above, it is necessary to make the opening port elongated in conjunction with downsizing the Op cabinet. The Q value becomes extremely small due to the increase in resistance. If the resonance Q value becomes extremely small, it means that the ability to radiate sound from the open port is lost, and as a result, the significance of providing the open port as a resonant duct is lost.
The very existence of the open port becomes meaningless.

In other words, if the device is made smaller, bass reproduction becomes virtually impossible.

[Problem that the invention seeks to solve]

As explained above, in conventional audio equipment,
Various efforts have been made to enable low frequency reproduction.

The planar bubble, rear open box-shaped baffle, and closed bubble shown in FIG. 29 are designed so that all sound radiated from the rear surface of the diaphragm is treated as disturbing sound and does not reach the listener in the front. However, when trying to improve bass reproduction characteristics using these methods, it is inevitable that the device (cabinet) becomes larger, and even when the device (cabinet) is enlarged, its low frequency reproduction characteristics are still insufficient.

The bass reflex type speaker system shown in FIG. 31 is configured to compensate for direct radiation sound from the front surface of the diaphragm, particularly in the bass range, by inverting the phase of rear sound using an open port. For this reason, a resonant system that is originally extremely difficult to handle occurs at two locations: the diaphragm and the aperture port.In order to fully obtain this bass reflex effect according to the basic settings, the mutual dependence conditions of these two resonant systems must be met. The optimum conditions for the system must be set extremely critically while taking into consideration the
Although various studies have been made as shown in Japanese Utility Model No. 670 and Japanese Utility Model Publication No. 54-35068, the difficulty in design has not been essentially solved by any of them.

In addition, regardless of whether an optimal design is achieved or not, the size of the cabinet has to be increased in order to improve the low-frequency reproduction characteristics.

There are also bass reflex type speaker systems in which the resonant frequency f of the port resonance system is intentionally lowered from the basic settings. However, even here, when trying to downsize the cabinet, there was a fatal drawback in that the port resonance system no longer contributed to acoustic radiation.

Therefore, with any of the above-mentioned conventional techniques, it was inevitable that the cabinet would become larger in order to obtain a certain level of bass reproduction ability.

As a result, the cabinet tends to have an appropriate volume in various applications such as halls, indoors, and automobiles, making it difficult to apply acoustic devices with excellent low-frequency reproduction characteristics.

This invention has been made in view of the above problems, and allows the volume and low-frequency reproduction characteristics of the cabinet constituting the acoustic device to be appropriately and independently set, and furthermore, it is possible to set the volume of the cabinet constituting the acoustic device and the low-frequency reproduction characteristics appropriately and independently. It is an object of the present invention to provide an audio device that can eliminate or reduce dependent conditions.

[Means for solving problems]

An acoustic device according to the present invention includes a resonator having a resonance radiation section for radiating sound due to resonance, a vibrator disposed in the resonator, and a vibrator driving means for driving the vibrator. . The vibrator has a vibrating body including a direct radiating part for directly radiating sound and a resonator driving part for driving the resonator, and the vibrator driving means is the vibrator. The present invention is characterized in that it has a drive control means that controls the drive state so as to equivalently reduce or nullify the internal impedance inherent in the drive.

[Effect]

According to the above configuration, the resonator is driven by the resonator driving part of the vibrating body, and therefore, sound is directly radiated from the direct radiation part of the vibrating body, and sound due to resonance is emitted from the resonance radiation part of the resonator. radiated.

Here, the vibrator has an inherent internal impedance, which is apparently reduced (preferably nullified) by the action of the drive control means in the vibrator drive means.

For this reason, the vibrator becomes an element that responds only to electrical drive signal input, and is no longer a resonant system.At the same time, the volume of the resonator is no longer a factor that affects the low frequency reproduction ability of the vibrator, so the cabinet Even when miniaturized, bass reproduction without distortion due to transient response can be achieved on the vibrator side. Also, Q near the resonant frequency of the resonator
Since the value can be set to a sufficiently large value, deep bass reproduction with sufficient sound pressure can be realized. Furthermore, this Q value can be set by the equivalent resistance of the resonant radiator (open port), the resonant frequency can be set by adjusting the equivalent mass of the resonant radiator (port), and the volume of the resonator can be adjusted to It ceases to be a factor that controls regeneration ability.

Furthermore, as shown in mechanical or electrical equivalent circuits, a vibration system using a vibrator and a resonance system using a resonator are
Since they can be treated more independently (preferably completely independently), the design interdependencies between the two can be reduced (preferably eliminated), and as shown in parentheses. However, since there is no problem with this, the design becomes extremely easy.

From the above, it is possible to simultaneously achieve miniaturization and deep bass reproduction, and it is also possible to design it easily.

〔Example〕

The present invention will now be described in detail with reference to the accompanying FIGS. 1 to 28. In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 shows the basic configuration of an embodiment of the present invention. As shown in FIG. 2A, in this embodiment, a Helmholtz resonator 10 having an open port 11 and a neck 12 forming a resonance radiation section is used as the resonator. In this Helmholtz resonator 10, air resonance occurs due to the closed cavity and the short tube with the open port 11 and neck 12. Then, it is determined as this resonance frequency. Here, C: the speed of sound S: the cross-sectional area of the open port]1, lll: the length of the neck 12 of the open port 11, ■=the volume of the cavity of the Helmholtz resonator]0.

In the acoustic device of this embodiment, a vibrator 20 consisting of a diaphragm 21 and a transducer 22 is attached. This converter 22 is connected to a vibrator driving device 30, which includes a negative impedance generating section 31 that generates an equivalent negative impedance component (-Z.) in the output impedance.

The configuration of the electrical equivalent circuit of this audio device is shown in Figure 1(b).
It looks like this. Here, the parallel resonant circuit Z is due to the equivalent motional impedance of the vibrator 20, r represents the equivalent resistance of the vibration system, S represents the equivalent stiffness of the vibration system, and m represents the equivalent mass of the vibration system. It shows. Moreover, the series resonant circuit Z2 is based on the equivalent motional impedance of the Helmholtz resonator]0 including the open port 11, r represents the equivalent resistance of the cavity of the resonator, S represents the equivalent stiffness of the cavity, rρ indicates the equivalent resistance of the open port, and mρ indicates the equivalent mass of the open port. In addition, A in the figure is a force coefficient. For example, when the vibrator is an electrodynamic direct radiation speaker,
If B is the magnetic flux density in the magnetic gap and ρ is the length of the voice coil conductor, then A=BJ7. Furthermore, Z in the figure
is the internal impedance of the converter 22, and for example, when the vibrator is an electrodynamic direct radiation speaker, it is mainly the DC resistance of the whirlpool coil and includes a small amount of inductance.

Next, the operation of the acoustic device having the configuration shown in FIG. 1 will be briefly explained.

Vibrator drive device 3 with negative impedance drive function
0, when a drive signal is given to the transducer 22 of the vibrator 20, the transducer 22 converts it electromechanically, and
is reciprocated back and forth (left and right in the figure), and this is converted into mechanical sound. Here, since the vibrator drive device 30 has a negative impedance drive function, the internal impedance specific to the converter 22 is effectively reduced (ideally, nullified). Therefore, the transducer 22 is connected to the vibrator drive device 3.
The diaphragm 21 is driven in faithful response to the drive signal from 0, and drive energy is independently given to the Helmholtz resonator 10. At this time, the front side of the diaphragm 21 (the left side in the figure) forms a direct radiating part for directly radiating sound to the outside, and the rear side of the diaphragm 21 (the right side in the figure) It constitutes a resonator driving section for driving the Lumholtz resonator 10.

Therefore, as shown by arrow a in the figure, sound is directly radiated from the diaphragm 21, and the air in the Helmholtz resonator 10 is resonated, so that deep and low sound with sufficient sound pressure is emitted from the resonance radiating section. Resonantly radiated. Then, by adjusting the air equivalent mass in the open port 11 and neck 12 in the Helmholtz resonator 10, this resonance frequency f is set lower than the reproduction frequency band of the vibrator 20p, and the open port l-
11 and neck 12 to an appropriate level by adjusting the equivalent resistance of the neck 12 to obtain an appropriate level of sound pressure from the opening port 11. For example, the frequency characteristic of the sound pressure as shown in FIG. Can you get it?

This situation will be explained below using equivalent circuits shown in FIGS. 3 and 4.

FIG. 3 is an electrical equivalent circuit that is simpler than FIG. 1(b). In other words, the equivalent resistance r of the cavity of the resonator]0
and the equivalent resistance r of the opening plate 11 and the screw plate 12
Since ρ is sufficiently small and its reciprocal is extremely large, this is an equivalent circuit diagram that ignores these. In FIG. 3, ■ is the current flowing through the circuit, and ■ and I2 are the currents flowing through the parallel resonant circuit Z and series resonant circuit Z2, respectively. When 2 = 2 - 2o, v has the following (2 ) to (4) hold true.

Ev-Eo・(Zl・Z2/(Z1+22))/['
(Z −Z / (Z +z) l +Z3
] ... (2) 11-Eo・ (Z2/(Z1+
Z2))/[fz −z /(z +z)l+z
3] ・ (3)■2=Eo・(Z1/(Z1+22
)) /Hz −z /(z 10z )l+z3
]...(4) Here, in order to simplify equations (3) and (4), if we set Z = Z - Z2/(Z1+22), the above equation (3) becomes I, = Eo/ ( Z, (]+Z3/Z4) l
・(5) becomes, and formula (4) becomes ■2-Eo/(Z2 (]+Z3/Z4))
...(6).

The following two points can be understood from these equations (5) and (6). First, as the value of Z3 approaches zero, the parallel resonant circuit Z1 on the vibrator side and the series resonant circuit Z2 on the resonator side both approach a short-circuited state in terms of alternating current.

The second is that the parallel resonant circuit Zj and the series resonant circuit Z2 are
-Zv-Z.

There is a relationship in which they influence each other through
The closer the value of is to zero, the more independent the parallel resonant circuit Z and the series resonant circuit Z2 become. and,
Ideally, z = z − zo =.

Assuming that v, equations (5) and (6) are respectively rl =
Eo/z1 ・, (7) I
-E. / Z 2 ... (8) - 23 -, and the parallel resonant circuit Z1 and the series resonant circuit Z2 are both short-circuited with an AC impedance of 7, and can be regarded as completely independent resonant systems.

In FIG.
The equivalent circuit v of FIG. 3 when =Z −Zo is shown.

First, when considering the resonant system by the vibrator 20 more strictly, the parallel resonant circuit Z1 based on the equivalent motional impedance is short-circuited at both ends with an alternating current impedance. Therefore, this parallel resonant circuit Z]
is, in effect, no longer a resonant circuit.

That is, the vibrator 20 linearly responds in real time to the drive signal input, and faithfully converts the electric signal (drive signal) into sound without any transient response.

Furthermore, with this vibrator 20, the concept of the lowest resonant frequency f that was simply present when the vibrator 20 was attached to the Helmholtz resonator 10 no longer exists. This is natural since both ends of the parallel resonant circuit Zl of the vibrator 20 are short-circuited in an alternating current manner with a seven-wire impedance. (Hereinafter, when we refer to the value equivalent to the lowest resonant frequency f of the vibrator 20, we are only temporarily referring to the above concept that has been essentially invalidated.)Furthermore, the vibrator 20
The Helmholtz resonator 10 and the Helmholtz resonator 10 are unrelated to each other, and the vibrator 20 and the open port 11 are also unrelated. It functions completely unrelated to the current (totally unrelated to the equivalent motional impedance of the port resonance system).

Furthermore, the parallel resonant circuit Z and the series resonant circuit Z2 coexist independently and independently of each other as a resonant system. Therefore, when the Helmholtz resonator 10 is designed to have a small volume in order to downsize the system, or when the aperture boat 11 and the neck 12 are designed to be elongated in order to lower the Q value of the port resonance system as described later. However, the design of the unit vibration system is not affected in any way, and the value equivalent to its lowest resonance frequency f is not affected at all. This allows easy design that does not depend on interdependent conditions.

From another perspective, this unit vibration system is effectively no longer a resonant system, so if the drive signal power is zero volts, the diaphragm 21 effectively becomes part of the wall of the resonator 10. It ends up. As a result, the existence of the diaphragm 21 can be ignored when considering the port resonance system.

From another perspective, it can be said that in the acoustic device of the present invention, the resonance system is only the port resonance system, and it exhibits the same single-peak characteristics as the conventional closed type.

Further, in the parallel resonant system, the Q value expressed as (load resistance)/(resonant impedance) becomes zero for the parallel resonant circuit Z1.

Q=0 in a unit vibration system has several other meanings.

First, the vibrator 20, which equivalently forms a parallel resonant circuit z1, has an input voltage E and a resistance A/r of the parallel resonant circuit Z1.
The speaker is driven by a current source called OvO. Electrically speaking, being in the current drive region means mechanically being in the speed drive region, and the frequency characteristics of sound waves near the lowest resonance frequency f of this speaker are 6 dB1.
It becomes 0ct.

On the other hand, the characteristics of the normal voltage drive state are 12 d
B/oct.

Second, the diaphragm 21 is fully damped. That is, control is performed to counteract the reaction caused by driving the diaphragm 21 by increasing or decreasing the drive current. Therefore, for example, the diaphragm 2
Even if an external force is applied to 1, a reverse driving force is applied at that moment until it is balanced with this external force (active servo)
.

Next, referring to FIG. 4 above, the Helmholtz resonator 1
0. A resonance system using the open port 11 and the neck 12 will be considered.

As shown in the figure, regarding this series resonant circuit Z2,
Both ends are short-circuited with zero Ω in AC.

= 27 - However, in this case, unlike the case of the parallel resonant circuit Z1 described above, the meaning as a resonant system is not lost at all. On the contrary, there is an effect that the Q value as a resonant system becomes extremely large (if it is close to the ideal state, the Q value becomes ■). In addition, this Helmholtz resonator 10, the opening port 11 and the neck 12
Although the virtual sound source (speaker) is actually driven by the displacement (vibration) of the diaphragm 21, the equivalent circuit in FIG. It is thought that driving energy is supplied from E. Therefore, by independently setting the resonant frequency and the resonant Q value on the resonator side, it is possible to reproduce deep bass with sufficient sound pressure despite the small size.

The series resonant circuit Z2 of the port resonance system also exists completely independently of the parallel resonant circuit Z1 of the unit vibration system. Therefore, the design specifications of the Helmholtz resonator 10 and the aperture port 11 are not affected by the design specifications of the vibrator 20, making it possible to easily design them without interdependent conditions.

Regarding this virtual speaker (acoustic source by the Helmholtz resonator 10), first, refer to (7) above.

From equation (8), the current ■ flowing through the converter 22 is I=11
+12°=, (1/Z +1/Z2)Eo -19). Also, from equation (8), the resonance frequency f of the open port 11
In the vicinity (state of port resonance system or Helmholt resonance), Z2 → 0 (
However, the current is actually damped by the resistance component), so the current flows sufficiently even with a voltage of minute amplitude.

On the other hand, the lowest resonant frequency f of the diaphragm 21. The equivalent value is the resonance frequency f of the open port 11. , the value of Zl is sufficiently large near the resonant frequency f. Therefore, equation (9) is I=11+
I2 vs. ■2, and most of the current flowing through the converter 22 contributes to driving the port resonance system (virtual speaker). Furthermore, since the port resonance system is driven with a small amplitude voltage (large current), the converter 22 in parallel with it is also driven with a small amplitude voltage, and therefore the diaphragm 21 operates with a small amplitude. I know that there is. Here, since the diaphragm 21 operates with a small amplitude, it has the effect of eliminating nonlinear distortion, which is common in large amplitude operations such as dynamic cone speakers, especially in the deep bass range.

Next, regarding the Q value of the resonance of the series resonant circuit Z2, unlike the parallel resonant circuit Z1, as described above, it is a series resonant system, so the Q value becomes infinite in the equivalent circuit shown in FIG. In this case, if the Q value of resonance is accurately calculated based on the equivalent circuit in Figure 1, it will be 1/2 Q-(m S ) /(r + rΩ)Ω
CC, but normally r and rΩ are extremely small, and if these are regarded as zero, the same result will be obtained. Therefore, this Q
By setting the value to an appropriate value, sufficient sound pressure can be obtained with this virtual speaker.

The Q value of this Helmholtz resonator 10 is generally easier to control than the Q value of the speaker unit.
It can be lowered if necessary. For example, when downsizing the Helmholtz resonator 10, at the resonant frequency 1/2 f = c (S/ΩV) /2π p of the resonant system of the open port 11, the cross-sectional area S of the open port may be reduced, or the neck This is achieved by increasing the length Ω. This means that in the audio device of the present invention, the fact that it is made smaller and is set to reproduce deep bass sounds is itself a factor in appropriately lowering the Q value. In other words, making the opening port 11 elongated increases the mechanical resistance (acoustic resistance) due to air friction, and therefore reduces A / r n in the equivalent circuit of Fig. 1(b). , the Q value of the series resonant circuit Z2 on the side of the Helmholtz resonator 10 and the open port 11 decreases,
As a result, damping characteristics are moderately improved. The point is that when the resonant frequency of the aperture port is intentionally lowered in a conventional bass reflex speaker system, the Q value of the resonant system becomes extremely small as the size is reduced, and the acoustic radiation ability of the port is eventually lost. This is a very good contrast compared to what had happened before.

In addition, it is also possible to reduce A2/r by inserting a sound absorbing material or the like into the Helmholtz resonator 10 to control the Q value as desired. What is important here is that under the condition of downsizing the resonator (cabinet), controlling the Q value of the port resonance system as described above will not have any effect on the unit vibration system. It is.

As is clear from the above description, according to the present invention, the frequency characteristics of sound pressure as shown in FIG. 2 can be easily realized with a compact device (cabinet). Here, near the lowest resonant frequency f of the unit vibration system expressed by the parallel resonant circuit Z1, its Q value is near zero, and near the resonant frequency f of the port resonant system, p of the series resonant circuit z2. The Q value can be set freely. In this case, the only resonant system in the device as a whole is the port resonant system,
Same as the conventional closed type, it has single peak characteristics. What is important is that the design of the unit vibration system and the design of the port resonance system can be performed independently. Thereby, the aperture port becomes a virtual speaker that is driven by the vibrator but acts independently of it.

Although this virtual speaker is realized with a small diameter corresponding to the aperture port diameter, its bass reproduction ability corresponds to an extremely large diameter speaker as a real speaker, and it is difficult to achieve dimensional efficiency or sound source concentration. has an extremely large effect. Of course, since you don't have to use actual speakers,
In that sense, cost efficiency is also extremely high. Furthermore, this virtual speaker does not have a real diaphragm, but is a virtual diaphragm made only of air, and can be said to be extremely ideal.

In addition, in the above explanation of the basic configuration, the ideal state is Z3-Zv-Zo=0 Although the explanation was made assuming that 0≦Z3〈Zv By doing so, the effects of the present invention can be fully obtained.

This is because the resonance Q value of the port resonance system increases as the value of Z3 decreases, and the correlation between the unit vibration system and the port resonance system decreases as the value of Z3 decreases. Therefore, for example, in an electrodynamic direct radiation speaker, if the internal resistance value of the voice coil is 8Ω, by creating an equivalent negative resistance of -4Ω and making the apparent resistance value 4Ω, the open port From the virtual speaker formed by 11, it is possible to realize sufficiently satisfactory bass reproduction.

Furthermore, it is not preferable to make the value of Z −Z −Zo negative by increasing the negative impedance too much. This is because when Z3 becomes negative, the entire circuit including the load becomes negatively resistive, causing oscillation. Therefore, if the value of internal impedance 2 changes due to heat generation during operation, etc., the negative impedance value should be set with some margin in advance, but the value of negative impedance should be set in advance according to temperature changes. Does it need to be changed (temperature compensated)?

Next, various aspects applicable to the basic configuration described above with reference to FIGS. 1 to 4 will be described.

First, the resonator is not limited to the one shown in FIG. 1(a). For example, the shape of the cavity is not limited to a sphere, but may be a rectangular parallelepiped, a cube, etc., and its volume is not particularly limited and can be designed independently of the unit vibration system. Therefore, the cabinet can be miniaturized with a small volume. In addition, the open port and neck that form the resonance radiation part are not limited to a cross-sectional shape,
For example, the sound path may protrude to the outside as shown in FIG. 1(a), or may be housed within the cavity.

Furthermore, the neck 12 may not be provided, and only an opening may be present. Furthermore, the openings may be dispersed into a plurality of pieces. Furthermore, the resonance frequency f 1 may be set as appropriate based on the correlation between the cross-sectional area of the open port and the neck length p 2 . moreover,
Since the cross-sectional area of the opening port can be set appropriately in relation to the length of the neck, by making the opening of the port small, the virtual speaker for low frequencies can be made small in diameter, concentrating the sound source and improving the sense of localization. Good too.

Regarding vibrators (electroacoustic transducers), as shown in Figures 5 to 12, various types can be applied, including electrodynamic types, electromagnetic types, piezoelectric types, and electrostatic types. can.

As shown in FIGS. 5 to 7, the diaphragm of an electrodynamic speaker (dynamic speaker) has a cone shape, a dome shape, a ribbon shape, a full drive type, and a bail driver shape. As shown in FIG. 5, the cone-shaped dynamic speaker has a cone-shaped cone 101 as a diaphragm,
A voice coil 10 is located near the top of this cone 101.
2 is fixed. And this voice coil '1.02
is inserted into a magnetic gap formed in the magnetic circuit 103. Note that in this cone-shaped dynamic speaker, non-motional impedance components mainly appear as resistance. The dome-shaped dynamic speaker shown in FIG. 6 has the following features, except that the diaphragm is a dome 104.
It is basically the same as the cone-shaped dynamic speaker shown in FIG.

The ribbon type dynamic speaker is constructed by disposing a ribbon diaphragm 105 in a magnetic gap of a magnetic circuit 103, as shown in FIG. In this type of ribbon, by passing a drive current in the longitudinal direction of the ribbon 05, it vibrates back and forth (up and down in the drawing) to generate sound waves. Therefore, the ribbon 105 serves both as a voice coil and as a diaphragm. Note that in this case as well, the non-monotonal impedance component mainly appears as resistance.

As shown in Figure 8, the fully-driven dynamic speaker is
Magnet plate 10 having openings 103a for radiating sound waves
3,103 are arranged in parallel, and the voice coil 10 is placed between them.
It is constructed by disposing a vibrating membrane 106 with two diaphragms. here,
The magnet plate 103 is magnetized so that the lines of magnetic force are almost parallel to the diaphragm 106, and the voice coil 102 is magnetized so that the lines of magnetic force are almost parallel to the diaphragm 106.
6 is fixed in a spiral shape.

Also in the bail driver type dynamic speaker shown in FIG. 9, the whistle coil]02 is disposed on the diaphragm]06''. That is, the diaphragm 106 has a bellows-like configuration, and the voice coil 02 is fixed thereto in a zigzag manner. According to this, the bellows of the diaphragm 106 alternately expands and contracts by applying a driving current to the heis coil 102.
Sound waves or radiated. In this speaker as well, non-motional impedance components mainly appear as resistance.

An example of an electromagnetic speaker is something like the one shown in Figure 10. As shown in the figure, a diaphragm 106 that is arranged to vibrate freely includes a magnetic material, and an iron core 108 around which a coil 107 is wound is provided in the vicinity of the diaphragm 106 . Here, when a driving current is passed through the coil 1.07, the diaphragm 106 is vibrated by the lines of magnetic force from the iron core 108, and sound waves are emitted in the vertical direction in the figure. Note that also in this type of speaker, the non-motional impedance component mainly appears as resistance.

As a piezoelectric speaker, there is one shown in FIG. 11. As shown in the figure, both ends of a bimorph 111 that vibrates due to the electrostrictive effect are fixed to a support 110, and a vibrating rod 112 is erected and fixed at the center thereof. The tip of the vibrating rod 112 is in contact with the center of the vibrating membrane 113 fixed to the support 110. In this speaker, the bimorph 111 bends due to the electrostrictive effect, and when the center vibrates up and down, this causes the vibration rod 1 to bend.
12 and is transmitted to the vibrating membrane 113.

Therefore, the vibrating membrane 113 can be vibrated in accordance with the drive current, and sound waves can be emitted. Note that in this speaker, non-motional impedance components mainly appear as capacitance.

There are electrostatic type speakers as shown in Figure 12. In general, the type shown in Figure 12 (a) is called a single type capacitor type, and the type shown in Figure 12 (b) is called a push-pull type capacitor type. It is called. In the same figure (a),
The vibrating membrane 121 is arranged in close proximity to a mesh-like electrode 122, and an input signal on which a bias E is superimposed is applied. Therefore, the vibrating membrane [2] is vibrated due to the electrostatic effect,
Can emit sound waves. At this time, since there is a reaction of the displacement current due to the vibration of the vibrating membrane 121, negative impedance (capacitance) can be equivalently generated using this reaction. In FIG. 2B, the vibrating membrane 121 is sandwiched between two mesh-like electrodes]-22. The operating principle is the same as that shown in FIG. 13(a), and the non-motional impedance component mainly appears as capacitance.

There are various types of negative impedance generating means as shown in FIGS. 13 to 21.

FIG. 13 shows its basic configuration. As shown in the figure, the output of an amplifier circuit 131 with a gain of A is applied to a load ZL formed by a speaker 132. Then, the current l flowing through this load Z is detected and positively fed back to the amplifier circuit 131 via a feedback circuit 133 with a transfer gain β. In this way, the output impedance Zo of the circuit can be obtained as Zo=28 (1-Aβ) - (10). If Aβ>1 in this equation (10), then Z
o becomes an open stable negative impedance. here,
Z8 is the impedance of the sensor that detects current.

FIG. 14 shows an example in which the current l is detected by a resistor R provided on the ground side of the speaker 32.

According to this, the output impedance Zo is the aforementioned (10
), Zo=R8(1-Aβ). Therefore, if Aβ>1, the apparent negative resistance component can be included in the output impedance. A specific example of such a circuit is shown in, for example, Japanese Patent Publication No. 59-51771.

FIG. 15 shows an example in which the current i is detected by a resistor R provided on the non-grounded side of the speaker 32.

This example also allows the output impedance Zo to include a negative resistance component. A specific example of such a circuit is shown in, for example, Japanese Patent Publication No. 54-33704. FIG. 16 shows a BTL connection, and 134 in the figure is an inverting circuit. In this circuit as well, the output impedance Zo is Zo=R(1-Aβ).

FIG. 17 is an example of detecting current i using a current probe. That is, since the current i forms an ambient magnetic field on the line, this is detected by the current probe 135 and the feedback circuit 1
It is fed back to the amplifier circuit 131 via 33.

FIG. 18 shows an example in which an integrator is used in the feedback circuit 133. That is, by integrating and detecting the voltage across the inductance L, it is possible to perform the same function as resistance detection. According to this circuit, the loss can be lowered near DC than when using the resistor R.

FIG. 19 is an example in which a differentiator is used in the feedback circuit 133. That is, by differentiating and detecting the voltage across the capacitance C, the same effect as resistance detection can be achieved. However, in this circuit, since the capacitance C is interposed in the drive system of the speaker 132, there is a problem that the drive signal of the DC component is cut off.

The example explained above is the output impedance Z.

Equivalently includes a negative resistance, and is applied when an electrodynamic or electromagnetic electroacoustic transducer is used. On the other hand, when a piezoelectric or electrostatic transducer (speaker) is used, the non-motional impedance component is capacitance. Therefore, it is necessary to equivalently include negative capacitance in the output impedance Zo.

FIG. 20 is a circuit diagram of an example, and the speaker 132 is an electrostatic or piezoelectric speaker. This speaker 13
Both ends of the capacitance C on the ground side of No. 2 are connected to the feedback circuit 13.
Connected to 3. According to this example, the output impedance Z. From the above-mentioned equation (10), Zo=C(1-Aβ).

When using an electroacoustic transducer that includes inductance as a non-motional impedance component, it is necessary to include equivalent negative inductance in the output impedance Zo. In addition, electrodynamic speakers and the like include a certain amount of inductance in addition to resistance as a non-motional impedance component, so if you want to nullify this inductance component, it is necessary to generate negative inductance. FIG. 21 is a circuit diagram of an example. As shown in the figure, both ends of the inductance L on the ground side of the speaker 132 are connected to a feedback circuit 133.

According to this example, the output impedance Zo is Zo=L (1-Aβ) becomes.

Next, embodiments of the present invention will be sequentially described.

FIG. 22 is a configuration diagram of an embodiment applied to a rectangular parallelepiped cabinet. As shown in the figure, a hole is made in the front of a rectangular parallelepiped-shaped cabinet 41, and an electrodynamic direct radiation speaker 42 is attached to the hole. The speaker 42 is composed of a cone-shaped diaphragm 43 and an electrodynamic transducer 44 provided near the top of the cone. Further, an open port 45 and a duct 46 are formed below the speaker 42 of the cabinet 41, and these form a virtual speaker for bass sounds unique to the present invention. The drive circuit 46 has a servo circuit 47 for driving a negative resistance, and the electrodynamic converter 44 is driven by this output.

Here, the electrodynamic converter 44 has a voice coil DC resistance R as its inherent internal impedance, and the drive circuit 46 has an equivalent negative resistance component (-R) in its output impedance. ,■ This allows the resistance R to be substantially nullified. Furthermore, R, LM, and CM are the motional impedances when the speaker 42 is electrically equivalently expressed. On the other hand, if the volume of the cabinet 41 is V, the cross-sectional area of the opening port 45 is Sl, and the neck length of the duct 46 is p, then the resonant frequency f is 1/2 f as shown in equation (1) above. =c (S/, &V), /2πp.

The equivalent operational configuration of the embodiment shown in FIG. 22 is as shown in FIG. 23. That is, a mid-high frequency speaker 42' formed by the speaker 42 and a virtual bass speaker 45' formed equivalently by the open port 45 are installed in a closed cabinet 41' having an infinite volume. is equivalent to . And a speaker 42' for medium and high frequencies
is an equivalently formed high-pass filter (HPF) 48
Normal (no active servo drive) via H
Connected to the amplifier 49, the bass speaker 45' is connected to an equivalent low-pass filter (LPF) 48L.
It is connected to the same amplifier 49 as above. (In addition, each filter 48H, 48L is a second-order HPF and a second-order L for convenience in order to emphasize the similarity with a normal network circuit.
It is expressed in PF. ) Here, the speaker 42 for medium and high frequencies
The lowest resonance frequency f of ' is determined by the equivalent motional impedances R, L, and CM, and the resonance Q value at that time is approximately zero, as shown above. And its characteristics are the virtual speaker 45 for bass.
It is completely unaffected by the design specifications on the ' side. Further, the resonance frequency f of the bass speaker 45' is determined by only the open port 45 and the duct 46, and the Q value of resonance at that time can be freely controlled.

As is clear from the above description, according to the embodiment shown in FIGS. 22 and 23, a virtual bass speaker is equivalently formed by the open port 45 and the duct 46. Since these are equivalent to being installed in a closed cabinet with infinite volume, extremely excellent bass reproduction characteristics can be achieved. The specifications of the speaker unit and the specifications of the cabinet can be freely designed without being restricted by each other, and the system can be made significantly smaller than any conventional speaker system.

Further, according to the present invention, as shown in FIG. 23, for example, a high-pass filter 48I (and a low-pass filter 48L) are equivalently formed, so that the configuration of the drive circuit can be simplified. For example, in a conventional two-way speaker system, a network of high-pass and low-pass filters had to be installed before the high- and low-frequency speakers. Since capacitance and inductance must be used, the cost of the drive circuit tends to be high, and the volume of the filter that occupies the drive circuit also tends to be large.Furthermore, the design has to be done separately. In the present invention, since these filters are formed equivalently, the problems of the prior art can also be solved.

Note that the sound pressure frequency characteristics of the vibrator and the resonator as a whole can be made arbitrary by increasing or decreasing the level of the input signal on the amplifier side. Since the sound radiation capabilities of both the vibrator and the resonator are sufficient, it is extremely easy to reproduce the sound pressure frequencies of the entire device in a broadband manner simply by adjusting the level of the input signal in this way. realizable.

Next, some specific examples prototyped by the inventor of the present invention will be described.

FIG. 24 is a circuit diagram of a drive circuit when an equivalent two-way speaker system is constructed using one speaker unit and one port resonance system (cabinet). In the same figure, the negative output impedance Zo is Z = R (1-Rb/Ra) S -〇, 22 (1-30/1.6) = -3,9 (
Ω) becomes. That is, in the circuit of FIG. 24, the equivalent output impedance is as shown in FIG. 25.

FIG. 26 is a circuit example of a negative resistance power amplifier with a low distortion factor. In the figure, the part A surrounded by the dotted line is the detection resistor R shown in FIGS. This is a part that is fed back to the input side, and corresponds to the circuit 133 etc. in FIG. 14. The reason for performing voltage-current conversion is to avoid being affected by the ground potential difference between the detection section and the input feedback section. In this circuit, the output impedance Z is Z = R(1-Rf/R,) S . Therefore, since Rf=30 and Ω, R<30
When Ω is equal to Ω, an equivalent negative resistance can be included in the output impedance zo.

FIG. 27 is a basic configuration diagram of a three-way speaker system using two speaker units and one port resonance system. According to this configuration, when the capacity of the Helmholtz resonator is 3.5 liters, the second
Excellent sound pressure frequency characteristics, as shown by the thick solid line in Figure 8, were obtained.

Here, the dashed-dotted line in the figure shows the output characteristics of the speaker for medium tones, and the dashed-double line shows the output characteristics of the tweeter for high-pitched sounds.

Further, the present inventor obtained the following results regarding a comparison between the effects of this invention and the effects of a bass reflex speaker system according to basic settings.

First, in the acoustic device according to the present invention, the volume of the cavity of the Helmholtz resonator was 6 liters, the inner diameter of the opening port was 3.3 am, and the neck base was 25 cm. Then, when a dynamic cone speaker was attached and negative resistance driving was performed, it was possible to reproduce deep bass up to f = 41 hertz.

p On the other hand, in a bass reflex speaker system that follows the basic settings, f = 5 as a dynamic cone speaker.
When using the latter with 0 Hz, Q = 0.5, and a diameter of 20 cm, it became possible to reproduce up to f = 41 Hz p when the cabinet capacity was 176 liters. Therefore, it has been found that the capacity of the cabinet can be increased to about 1/30 times for the same level of heavy bass reproduction.

〔Effect of the invention〕

As described above in detail, according to the present invention, the inherent internal impedance of the vibrator is apparently reduced (preferably disabled) by the action of the drive control means in the vibrator drive means. ).

For this reason, the vibrator becomes an element that responds only to electrical drive signal input, performs ideal operation without causing any -cut transient response, and the resonant system of this vibrator is essentially no longer a resonant system. , it simply becomes equivalent to the wall of the resonator. Therefore, although the resonator is driven by the vibrator, when viewed from the drive control means, it becomes an element to which drive energy is supplied completely independently of the vibrator, and there is no influence of the vibrator impedance, so the resonator The resonance Q value of the resonator becomes extremely large, and its acoustic radiation ability becomes strong, and even if the resonance Q value of the resonator decreases due to other factors, there is sufficient margin.

In addition, the low-frequency reproduction characteristics of the vibrator are not affected by the volume of the resonator, and the resonant frequency of the resonator can be set only by the equivalent mass of the resonance radiating part, so the volume of the resonator also depends on the volume. The resonator itself is no longer a factor that controls the low-frequency reproduction characteristics, and as a result, the low-frequency reproduction characteristics of the device can be set completely independent of the device volume, making it easy to create a compact acoustic device that can reproduce deep bass. This can be realized.

Furthermore, as shown in the mechanical or electrical equivalent circuit, a resonant system using a vibrator and a resonant system using a resonator,
Since it becomes possible to handle them more independently (preferably completely independently), it is easier to design any band by reducing the mutual dependence conditions between them (preferably eliminating the mutual dependence conditions). can be done without causing any problems.

Further, the acoustic device of the present invention can be widely applied not only as an audio speaker system but also as a sounding body for electronic musical instruments, electric musical instruments, or other sounding bodies.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the basic configuration of an embodiment of the present invention, Fig. 2 is a frequency characteristic diagram of sound pressure, and Fig. 3 is an electrical equivalent circuit diagram of Fig. 1(a). Figure 4 is an equivalent circuit diagram when 23 in Figure 3 is set to zero. Figures 5 to 9 are diagrams explaining some examples of electrodynamic speakers. Figure 10 is an electromagnetic speaker. 11 is a cross-sectional view illustrating an example of a piezoelectric speaker, FIG. 12 is a circuit diagram illustrating an example of an electrostatic speaker, and FIG. 13 is an equivalently negative 14 to 19 are circuit diagrams of a circuit that generates a uniform resistance. FIG. 20 is a circuit diagram of a circuit that generates a uniform capantance. FIG. 21 is a circuit diagram of a circuit that generates an equivalent inductance, FIG. 22 is a configuration diagram of an acoustic device according to a more specific embodiment, and FIG. 23 is an equivalent operational configuration of the device in FIG. 22. Fig. 24 is a circuit diagram when a two-way speaker system is realized using one vibrator, and Fig. 25 explains the output impedance equivalently formed in Fig. 24. Figure 26 is a circuit diagram of a low distortion negative resistance power amplifier, Figure 27 is a configuration diagram when a 3-way speaker system is realized using two vibrators, and Figure 28 is a circuit diagram of a negative resistance power amplifier with low distortion. , second
Figure 7 is a diagram showing the frequency characteristics of sound pressure by a speaker system, Figure 29 is a cross-sectional view of a baffle used in a conventional speaker system, Figure 30 is an electrical equivalent circuit diagram of a closed speaker system, Figure 31 Figure 32 is a diagram illustrating the main parts of a bass reflex speaker system, Figure 32 is a diagram comparing and explaining the sound pressure frequency characteristics of conventional examples, Figure 33 is an electrical equivalent circuit of a bass reflex speaker system. It is a diagram. DESCRIPTION OF SYMBOLS 10... Helmholtz resonator, 11... Open lobe, 12... Neck, 20... Vibrator, 21... Vibration plate, 22... Transducer, 30... Vibrator drive device, 3
1. Drive control means (negative impedance generating section), Z
o...Output impedance, ZV...Internal impedance (non-motional impedance component). Patent Applicant: Yoshiki Hase, Patent Attorney, Yamaha Co., Ltd. Cone-type dynamic speaker Figure 5: Dome-type dynamic speaker Figure 6: Ribbon-type dynamic speaker Figure 7: Fully-driven dynamic speaker Figure 8: Electromagnetic type Speaker Fig. 10 Piezoelectric type speaker Fig. 11 Input electrostatic speaker Fig. 12 Conventional speakers Fig. ) (b)
Bass reflex type NUBICA system Figure 31 Electrical equivalent circuit of bass reflex Figure 33

Claims (13)

[Claims] 1. A vibration device comprising: a resonator having a resonance radiation section for radiating sound due to resonance; a direct radiation section for directly radiating sound; and a resonator drive section for driving the resonator. a vibrator disposed in the resonator; a drive control means for controlling a drive state to equivalently reduce or nullify internal impedance specific to the vibrator; An acoustic device comprising: a vibrator drive means for driving a vibrator; 2. The resonator includes a cabinet having a first opening in which the vibrator is disposed and a second opening forming the resonance radiation section, and the vibrating body of the vibrator is located on the outer surface side of the cabinet. 2. The acoustic device according to claim 1, wherein a portion of the cabinet constitutes the direct radiation section, and an inner surface of the cabinet constitutes the resonator drive section. 3. 2. The acoustic device according to claim 1, wherein the resonant frequency of the resonator is different from the resonant frequency of the vibrator when the vibrator is simply disposed in the resonator. 4. 2. The acoustic device according to claim 1, wherein the resonant frequency of the resonator is lower than the resonant frequency of the vibrator when the vibrator is simply disposed in the resonator. 5. 3. The acoustic device according to claim 2, wherein the resonator is a Helmholtz resonator having the second opening as an opening port. 6. 6. The acoustic device of claim 5, wherein the open port has a cylindrical neck. 7. 2. The acoustic device according to claim 1, wherein the vibrator is an electrodynamic electroacoustic transducer. 8. 2. The acoustic device according to claim 1, wherein the vibrator is an electromagnetic electroacoustic transducer. 9. 2. The acoustic device according to claim 1, wherein the vibrator is an electrostatic electroacoustic transducer. 10. 2. The acoustic device according to claim 1, wherein the vibrator is a piezoelectric electroacoustic transducer. 11. 2. The acoustic device according to claim 1, wherein the drive control means is a negative impedance generating means that equivalently generates a negative impedance component in the output impedance of the vibrator driving means. 12. The negative impedance generating means is configured to positively feed back a signal corresponding to the drive current of the vibrator to the input side of the vibrator driving means to equivalently generate a negative impedance component. An acoustic device according to claim 11. 13. 13. The acoustic device according to claim 12, wherein the negative impedance generating means is configured to equivalently generate a negative resistance component in the output impedance.